Non-aqueous electrolytic solution and lithium secondary battery

ABSTRACT

A non-aqueous electrolytic solution favorably employable for a lithium secondary battery employs a non-aqueous electrolytic solution which comprises a non-aqueous solvent and an electrolyte which further contains 0.001 to 0.8 weight % of a biphenyl derivative having the formula:  
                 
 
     in which each of Y 1  and Y 2  represents hydroxyl, alkoxy, hydrocarbyl, hydrogen, acyloxy, alkoxycarbonyloxy, alkylsulfonyloxy, or halogen, and each of p and q is an integer of 1 to 3.

FIELD OF THE INVENTION

[0001] The present invention relates to a non-aqueous electrolyticsolution and a lithium secondary battery employing the non-aqueouselectrolytic solution. In particular, the invention relates to a lithiumsecondary battery having improved electric capacity and cyclingperformance, and a non-aqueous electrolytic solution which isadvantageously employable for preparing the lithium secondary battery.

BACKGROUND OF THE INVENTION

[0002] At present, potable small electronic devices such as personalcomputers, cellular phones, and video recorders equipped with camera arewidely used, and a small sized secondary battery having light weight andhigh electric capacity is desired to provide an electric source fordriving such small electronic devices. From the view-points of smallsize, light weight, and high electric capacity, a lithium secondarybattery is paid attention.

[0003] The lithium secondary battery employs a positive active electrodematerial comprising a complex oxide such as lithium cobaltate, lithiumnickelate, or lithium manganate, a negative active electrode materialcomprising a carbonaceous material such as graphite into which lithiumions are able to intercalate and from which lithium ions are able toescape, and a non-aqueous electrolytic solution of a lithium salt in anon-aqueous solvent comprising a cyclic carbonate and a linear chaincarbonate. The lithium secondary battery is now studied for improvingits performances.

[0004] The lithium secondary battery employing LiCoO₂, LiOO₄, or LiNiO₂as the positive electrode active material is generally used under suchcondition that the electric charge-discharge procedure is repeated inthe range up to the maximum operating voltage exceeding 4.1 V. In theprocedure, the conventional lithium secondary battery is apt togradually lower in its electric capacity when the charge-discharge cycleis repeated for a long period. It is supposed that this trouble iscaused by oxidative decomposition of a portion of the non-aqueoussolvent of the electrolytic solution on the surface of the positiveelectrode when the maxim operating voltage exceeds 4.1 V, and thedecomposition product disturbs the desired electrochemical reaction inthe battery. Therefore, the conventional lithium secondary batteries arenot satisfactory in their battery performances such as the cyclingperformance and an electric capacity when the batteries are operated inthe charge-discharge cycles of which maxi operating voltage exceeds 4.1V.

[0005] U.S. Pat. No. 5,879,834 describes incorporation of an aromaticadditive such as biphenyl, 1,3-chlorothiophene, or furan into anon-aqueous rechargeable lithium battery. The additive is used in anamount of about 1% to 4%. The aromatic additive is electrochemicallypolymerized at abnormally high voltages, thereby increasing the internalresistance of the battery and thus protecting it.

[0006] U.S. Pat. No. 6,074,777 describes incorporation of an aromaticadditive such as phenyl-R-phenyl compounds (R=aliphatic hydrocarbon),fluorine-substituted biphenyl compounds, or 3-thiopheneacetonitrile intoa non-aqueous rechargeable lithium battery. The additive is preferablyused in an amount of about 2.5%.

[0007] It is an object of the invention to provide a non-aqueouselectrolytic solution which is favorably employable for a lithiumsecondary battery and which shows high battery performances such as highelectric capacity and high cycling performance, particularly, under theconditions that the maximum operating voltage exceeds 4.1 V and/or thebattery is used at high temperatures such as 40° C. or higher.

[0008] It is another object of the invention to provide a lithiumsecondary battery which shows high battery performances such as highelectric capacity and high cycling performance, particularly, under theconditions that the maximum operating voltage exceeds 4.1 V and/or thebattery is used at high temperatures such as 40° C. or higher.

SUMMARY OF THE INVENTION

[0009] The present invention resides in a non-aqueous electrolyticsolution which comprises a non-aqueous solvent and an electrolyte whichfurther contains 0.001 to 0.8 weight % of a biphenyl derivative havingthe formula (I):

[0010] in which each of Y¹ and Y² independently represents a hydroxylgroup, an alkoxy group, a hydrocarbyl group, a hydrogen atom, an acyloxygroup, an alkoxycarbonyloxy group, an alkylsulfonyloxy group or ahalogen atom, and each of p and q independently is an integer of 1 to 3.

[0011] More preferably, the biphenyl derivative has the followingformula (II):

[0012] in which Y represents a hydroxyl group, an alkoxy group, ahydrocarbyl group, a hydrogen atom, an acyloxy group, analkoxycarbonyloxy group, or an alkylsulfonyloxy group

[0013] In the formulas (I) and (II), the alkoxy group preferably has aformula of —OR¹ in which R¹ is a hydrocarbyl group having 1 to 12 carbonatoms; the hydrocarbyl group preferably has a formula of -R² in which R²has 1 to 12 carbon atoms; the acyloxy group preferably has a formula of—O—C(═O)-R³ in which R³ is a hydrocarbyl group having 1 to 12 carbonatoms; the alkoxycarbonyl group preferably has a formula of—O—C(═O)—O-R⁴ in which R⁴ is a hydrocarbyl group having 1 to 12 carbonatoms; the alkylsulfonyloxy group preferably has a formula of—O—S(═O)₂-R⁵ in which R⁵ is a hydrocarbyl group having 1 to 12 carbonatoms; and a halogen atom can be F, Cl, Br or I.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The non-aqueous electrolytic solution of the invention containsthe biphenyl derivative of the formula (I) or the formula (II) in a verysmall amount such as 0.001 to 0.8 wt. %, preferably 0.01 to 0.5 wt. %,more preferably 0.03 to 0.3 wt. %. If the amount of the biphenylderivative exceeds the upper limit, the incorporation of the biphenylderivative does not give satisfactory improvements of the batteryperformances such as high electric capacity and high cyclingperformance. If the amount of the biphenyl derivative is less than 0.001wt %., no noticeable improvement is observed.

[0015] It is supposed that the appropriate amount of the biphenylderivative forms an appropriately thin film on the positive electrodeupon its decomposition thereon to improve the battery performances,particularly, the cycling performance. If the amount of the additive,i.e., the biphenyl derivative, is too larger, a thick film is producedon the positive electrode, and the thick film disturbs the cyclingperformance of the battery.

[0016] In the biphenyl derivatives of the formula (I) or the formula(II), the substituent such as Y¹, Y² or Y³ preferably is a hydrogenatom, a hydroxyl group, a linear chain alkoxy group such as methoxy,ethoxy, propoxy, or butoxy, a branched chain alkoxy group such asisopropoxy or isobutoxy, a cycloalkoxy group such as cyclopropoxy orcyclohexyloxy, an aryloxy group such as phenoxy, p-tolyloxy, orbiphenylyloxy, a linear chain alkyl group such as methyl, ethyl, propyl,or butyl, a branched chain alkyl group such as isopropyl or isobutyl, acycloalkyl group such as cyclopropyl or cyclohexyl, an aryl group suchas phenyl, p-tolyl, or biphenylyl, an acyloxy group such as acetyloxy,propionylox, acryloyloxy, or benzoyloxy, an alkoxycarbonyloxy group suchas methoxycarbonyloxy, ethoxycarbonyloxy, phenoxycarbonyloxy, orbenzyloxycarbonyloxy, or an alkylsulfonyloxy group such asmethanesulfonyloxy, ethanesulfonyloxy, or benzensulfonyloxy.

[0017] Preferred are biphenyl derivatives of the formula (II). Examplesof the biphenyl derivatives of the formula (II) include2-hydroxybiphenyl, 3-hydroxybiphenyl, 4-hydroxybiphenyl,2-methoxybiphenyl, 3-methoxybiphenyl, 4-methoxybiphenyl,p-diphenylylphenyl ether, 4-biphenylyl, p-tolyl ether 4-biphenylylether, 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl,4-ethylbiphenyl, 4-propylbiphenyl, 4-isopropylbiphenyl, 4-butylbiphenyl,4-t-butylbiphenyl, 4-cyclohexylbiphenyl, o-terphenyl (Y=phenyl),m-terphenyl, p-terphenyl, 2-methyl-o-terphenyl (Y=tosyl), o-qarterphenyl(Y=biphenylyl), biphenyl, 4-biphenylyl acetate (Y=acetyloxy),4-biphenylyl benzoate (Y=benzyloxy), 4-biphenylyl benzylcarboxylate(Y=benzylcarbonyloxy), 2-biphenylyl propionate, 2-biphenylylmethylcarbonate (Y=methoxycarbonyloxy), 4-biphenylyl methylcarbonate,4-biphenylyl butylcarbonate (Y=butoxycarbonyloxy),4-methanesulfonyloxybiphenyl, 4ethanesulfonyloxybiphenyl, and4-benzenesulfonyloxybiphenyl.

[0018] The non-aqueous electrolytic solution of the invention comprisesa non-aqueous solvent which preferably comprises a combination of acyclic carbonate and a linear chain carbonate. The non-aqueous solventis also preferred to comprise a high dielectric constant solvent such asethylene carbonate, propylene carbonate, or butylene carbonate, and alow viscosity solvent such as dimethyl carbonate, methyl ethylcarbonate, diethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran,1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane,1,2-dibutoxyethane, γ-butyrolactone, acetonitrile, methyl propionate, ordimethylformamide. The high dielectric constant solvent and the lowviscosity solvent are preferably employed in a volume ratio of 1:9 to4:1, preferably, 1:4 to 7:3 (former:latter).

[0019] The non-aqueous solvent may contain a phosphate ester such astriethyl phosphate, tributyl phosphate, or trioctyl phosphate, vinylenecarbonate, and 1,3-propanesultone.

[0020] Examples of the electrolytes include LiPFG, LiPF₄, LiClO₄,LiN(SO₂CF₃)₂, LiN(SO₂CF₃)₃, LiC(SO₂CF₃)₃, LiPF, (CF₃)₃, LiPF₃ (C₂F₅)₃LiPF₄ C₂F₅)₂, LiPF₃ (iso-C₃F₇)₃, and LiPF₅(iso-CF₇) The electrolytes canbe employed singly or in combination. Generally, the electrolyte can bedissolved in the non-aqueous solvent in such an amount to give anelectrolytic solution of 0.1 M to 3 M, preferably 0.5 M to 1.5 M.

[0021] The non-aqueous electrolytic solution of the invention isprepared, for instance, by dissolving the electrolyte in a mixture of acyclic carbonate and a linear chain carbonate.

[0022] The non-aqueous electrolytic solution of the invention ispreferably employed for manufacturing a lithium secondary battery.Materials other than the electrolytic solution are known for themanufacture lithium secondary battery, and the known materials can beemployed without specific limitations.

[0023] For instance, the positive electrode active material can be acomplex metal oxide comprising lithium and at least one metal elementselected from the group consisting of cobalt, nickel, manganese,chromium, vanadium and iron. Examples of the complex metal oxidesinclude LiCoO₂, LiMn_(2O) ₄, and LiNiO₂.

[0024] The positive electrode can be prepared by kneading a mixture ofthe above-mentioned positive electrode active material, anelectro-conductive agent such as acetylene black or carbon black, abinder such as poly(vinylidene fluoride) (PVDF) orpolytetrafluoroethylene (PIEs), and an 1-methyl-2-pyrrolidone solvent toproduce a positive electrode composition, coating the positive electrodecomposition on a metal plate such as aluminum foil or stainless sheet,drying the coated composition, molding the dry film under pressure, andthen heating the molded film under reduced pressure at 50 to 250° C. for2 hours The negative electrode preferably comprises a natural orartificial graphite having a lattice spacing (or lattice distance, interms of 402) of 0.335 to 0.340 nm. Other known negative electrodematerials such as thermally decomposed carbonaceous articles, cokes,thermally fired polymer articles, and carbon fibers can be employed.

[0025] The negative electrode can be prepared by kneading a mixture ofthe above-mentioned graphite, a binder such as PVDF, PTFE orethylene-propylene diene terpolymer (EPDM), and an1-methyl-2-pyrrolidone solvent to produce a negative electrodecomposition, coating the negative electrode composition on a metal platesuch as aluminum foil or stainless sheet, drying the coated compositionat 50 to 250°.

[0026] There are no specific limitations with respect to the structureof the lithium secondary battery of the invention. For instance, thelithium secondary battery can be a battery of coin type comprising apositive electrode, a negative electrode, plural separators, and theelectrolytic solution, or a cylindrical, prismatic or laminate battery.

[0027] The lithium secondary battery of the invention is preferablyemployed in the operating voltage range having the maximum operatingvoltage exceeding 4.1 V, more preferably 4.2 V, most preferably 4.3 V.The cut-off voltage preferably is higher than 2.0 V, more preferably ishigher than 2.5 V. The battery is generally operated at a constantcurrent discharge of 0.1 to 2 C. The charge-discharge cycles arepreferably operated at temperatures of 20 to 100° C., more preferably 40to 80° C.

EXAMPLE 1

[0028] 1) Preparation of electrolytic solution

[0029] A non-aqueous solvent, i.e., a mixture (1:2, volume ratio) ofpropylene carbonate (PC) and diethyl carbonate (DEC), was prepared.Subsequently, LiPF₆ was dissolved in the non-aqueous solvent to give a1M concentration solution. Further, biphenyl was added to give a 0.1 wt.% solution. Thus, an electrolytic solution was prepared.

[0030] 2) Preparation of lithium secondary battery and measurement ofbattery performances

[0031] LiCoO₂ (positive electrode active material, 80 wt %), acetyleneblack (electro-conductive material, 10 wt %), and poly(vinylidenefluoride) (binder, 10 wt. %) were mixed. The resulting mixture wasdiluted with 1-methyl-2-pyrrolidone. Thus produced positive electrodecomposition was coated on aluminum foil, dried, molded under pressure,and heated to give a positive electrode.

[0032] Natural graphite (d₀₀₂=0.3354, 90 wt. %) and poly(vinylidenefluoride) (binder, 10 wt. %) were mixed. The mixture was then dilutedwith 1-methyl-2-pyrrolidone. Thus produced negative electrodecomposition was coated on copper foil, dried, molded under pressure, andheated, to give a negative electrode.

[0033] The positive and negative electrodes, a micro-porouspolypropylene film separator, and the electrolytic solution werecombined to give a coin-type battery (diameter: 20 mm, thickness: 3.2mm).

[0034] The coin-type battery was charged for 6 hours at a hightemperature (40° C.) with a constant electric current (0.8 mA) to reach4.3 V and then the charging was continued under a constant voltage of4.3 V. Subsequently, the battery was discharged to give a constantelectric current (0.8 mA). The discharge was continued to give aterminal voltage of 2.7 V. The charge-discharge cycle was repeated 100times.

[0035] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0036] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.5% of the initial discharge capacity. The lowtemperature characteristics were satisfactory.

COMPARISON EXAMPLE 1

[0037] A secondary battery was prepared in the same manner as in Example1, except for adding no biphenyl to the solvent.

[0038] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0039] After the 100 cycle charge-discharge procedure, the dischargecapacity was 63.8% of the initial discharge capacity.

COMPARISON EXAMPLE 2

[0040] A secondary battery was prepared in the same manner as inComparison Example 1.

[0041] Thus prepared battery was charged in the same manner as inExample 1, except that the charging procedure was performed to reach 4.1V and then the charging was continued under a constant voltage of 4.1 V.

[0042] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0043] The initial discharge capacity was 0.90 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0044] After the 100 cycle charge-discharge procedure, the dischargecapacity was 75.3% of the initial discharge capacity.

COMPARISON EXAMPLE 3

[0045] A secondary battery was prepared in the same manner as in Example1, except that biphenyl was added to the solvent in an amount of 2.5 wt.%.

[0046] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0047] The initial discharge capacity was 1.00 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0048] After the 100 cycle charge-discharge procedure, the dischargecapacity was 20.7% of the initial discharge capacity.

COMPARISON EXAMPLE 4

[0049] A secondary battery was prepared in the same manner as in Example1, except that biphenyl was added to the solvent in an amount of 2.5 wt.%.

[0050] Thus prepared battery was charged in the same manner as inExample 1, except that the charging procedure was performed at 20° C.(ambient temperature).

[0051] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0052] The initial discharge capacity was 1.00 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0053] After the 100 cycle charge-discharge procedure, the dischargecapacity was 62.20% of the initial discharge capacity.

COMPARISON EXAMPLE 5

[0054] A secondary battery was prepared in the same manner as in Example1, except that biphenyl was added to the solvent in an amount of 2.5 wt.%.

[0055] Thus prepared battery was charged in the same manner as inExample 1, except that the charging procedure was performed to reach 4.1V and then the charging was continued under a constant voltage of 4.1 V.

[0056] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0057] The initial discharge capacity was 0.90 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0058] After the 100 cycle charge-discharge procedure, the dischargecapacity was 73.7%. of the initial discharge capacity.

COMPARISON EXAMPLE 6

[0059] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt % of biphenyl was replaced with 2.5 wt. % of2,2-diphenylpropane.

[0060] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0061] The initial discharge capacity was 1.00 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0062] After the 100 cycle charge-discharge procedure, the dischargecapacity was 58.8% of the initial discharge capacity.

EXAMPLE 2

[0063] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.05 wt. % of4-methoxybiphenyl.

[0064] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0065] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0066] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.8% of the initial discharge capacity.

EXAMPLE 3

[0067] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt. % of4-methoxybiphenyl.

[0068] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0069] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0070] After the 100 cycle charge-discharge procedure, the dischargecapacity was 92.4% of the initial discharge capacity.

EXAMPLE 4

[0071] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.3 wt. % of4-methoxybiphenyl.

[0072] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0073] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0074] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.7% of the initial discharge capacity.

EXAMPLE 5

[0075] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.5 wt. % of4-methoxybiphenyl.

[0076] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0077] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0078] After the 100 cycle charge-discharge procedure, the dischargecapacity was 88.8% of the initial discharge capacity.

EXAMPLE 6

[0079] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt. % of4-hydroxybiphenyl.

[0080] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0081] The initial discharge capacity was 1.00 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0082] After the 100 cycle charge-discharge procedure, the dischargecapacity was 91.4% of the initial discharge capacity.

EXAMPLE 7

[0083] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt. % ofo-terphenyl.

[0084] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure-

[0085] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0086] After the 100 cycle charge-discharge procedure, the dischargecapacity was 91.2% of the initial discharge capacity.

EXAMPLE 8

[0087] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt % of4-biphenylyl acetate.

[0088] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0089] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0090] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.1% of the initial discharge capacity.

EXAMPLE 9

[0091] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt. % of4-biphenylyl methylcarbonate.

[0092] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0093] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0094] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.7% of the initial discharge capacity.

EXAMPLE 10

[0095] A secondary battery was prepared in the same manner as in Example1, except that 0.1 wt. % of biphenyl was replaced with 0.1 wt. % of4-methanesulfonyloxybiphenyl.

[0096] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0097] The initial discharge capacity was 1.03 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0098] After the 100 cycle charge-discharge procedure, the dischargecapacity was 90.3% of the initial discharge capacity

EXAMPLE 11

[0099] A secondary battery was prepared in the same manner as in Example1, except that the natural graphite was replaced with artificialgraphite.

[0100] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure

[0101] The initial discharge capacity was 1.06 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0102] After the 100 cycle charge-discharge procedure, the dischargecapacity was 93.2% of the initial discharge capacity.

EXAMPLE 12

[0103] A secondary battery was prepared in the same manner as in Example11, except that LiCo% of the positive electrode material was replacedwith LiMn₂O₄.

[0104] The prepared secondary battery was subjected to the 100 cyclecharge-discharge procedure.

[0105] The initial discharge capacity was 0.85 (relative value based on1 for that measured in a battery of Comparison Example 1 which containedno biphenyl in the electrolytic solution).

[0106] After the 100 cycle charge-discharge procedure, the dischargecapacity was 93.0% of the initial discharge capacity.

[0107] The preparations and evaluations of the batteries of Examples 1to 12 and Comparison Examples 1 to 6 are summarized in Table 1. In Table1, the standard conditions are as follows:

[0108] Positive electrode: LiCoO₂

[0109] Negative electrode: natural graphite

[0110] Terminal voltage for charging: 4.3 V

[0111] Cycle temperature: 40° C.

[0112] Electrolytic solution: 1M LiPF₆ in EC/DEC=1/2 TABLE 1 AdditiveInitial discharge 100 Cycle Example (wt. %) capacity (relative)retention Ex. 1 biphenyl (0.1) 1.03 90.5% Com.1 none 1   63.8% Com.2*none 0.90 75.3% Com.3 biphenyl (2.5) 1.00 20.7% Com.4* biphenyl (2.5)1.00 62.2% Com.5* biphenyl (2.5) 0.90 73.7% Com.6 2,2-diphenyl- 1.0058.8% propane (2.5) Ex. 2 4-methoxy- 1.03 90.8% biphenyl (0.05) Ex. 34-methoxy- 1.03 92.4% biphenyl (0.1) Ex. 4 4-methoxy- 1.03 90.7%biphenyl (0.3) Ex. 5 4-methoxy- 1.03 88.8% biphenyl (0.5) Ex. 64-hydroxy- 1.00 91.4% biphenyl (0.1) Ex. 7 o-terphenyl (0.1) 1.03 91.2%Ex. 8 4-biphenylyl 1.03 90.1% acetate (0.1) Ex. 9 4-biphenylyl methyl-1.03 90.7% carbonate (0.1) Ex. 10 4-methanesulfonyloxy- 1.03 90.3%biphenyl (0.1) Ex. 11* biphenyl (0.1) 1.06 93.2% Ex. 12* biphenyl (0.1)0.85 93.0%

[0113] Remarks:

[0114] Com. Ex 2 (Terminal voltage for charging: 4.1 V)

[0115] Com. Ex. 4 (Cycle temperature: 20° C.)

[0116] Com. Ex. 5 (Terminal voltage for charging: 4.1 V)

[0117] Example 11 (Negative electrode: artificial graphite)

[0118] Example 12 (Negative electrode: artificial graphite,

[0119] Positive electrode: LiMn₂O₄)

What is claimed is:
 1. A non-aqueous electrolytic solution whichcomprises a non-aqueous solvent and an electrolyte which furthercontains 0.001 to 0.8 weight % of a biphenyl derivative having thefollowing formula:

in which each of Y¹ and Y² independently represents a hydroxyl group, analkoxy group, a hydrocarbyl group, a hydrogen atom, an acyloxy group, analkoxycarbonyloxy group, an alkylsulfonyloxy group or a halogen atom,and each of p and q independently is an integer of 1 to
 3. 2. Thenon-aqueous electrolytic solution of claim 1, wherein the biphenylderivative has the following formula:

in which Y represents a hydroxyl group, an alkoxy group, a hydrocarbylgroup, a hydrogen atom, an acyloxy group, an alkoxycarbonyloxy group, oran alkylsulfonyloxy group.
 3. The non-aqueous electrolytic solution ofclaim 1, wherein the amount of the biphenyl derivative is in the rangeof 0.01 to 0.5 weight %.
 4. The non-aqueous electrolytic solution ofclaim 2, wherein the amount of the biphenyl derivative is in the rangeof 0.01 to 0.5 weight %.
 5. The non-aqueous electrolytic solution ofclaim 1, wherein the non-aqueous solvent comprises a combination of acyclic carbonate and a linear chain carbonate.
 6. The non-aqueouselectrolytic solution of claim 2, wherein the non-aqueous solventcomprises a combination of a cyclic carbonate and a linear chaincarbonate
 7. The non-aqueous electrolytic solution of claim 1, whereinthe non-aqueous solvent comprises a high dielectric constant solventwhich is selected from the group consisting of ethylene carbonate,propylene carbonate, and butylene carbonate, and a low viscosity solventwhich is selected from the group consisting of dimethyl carbonate,methyl ethyl carbonate, diethyl carbonate, tetrahydrofuran,2-methyltetrahydrofuran, 1,4-diode, 1,2-dimethoxyethane,1,2-diethoxyethane, 1,2-dibutoxyethane, γ-butyrolactone, acetonitrile,methyl propionate, and dimethylformamide.
 8. The non-aqueouselectrolytic solution of claim 2, wherein the non-aqueous solventcomprises a high dielectric constant solvent which is selected from thegroup consisting of ethylene carbonate, propylene carbonate, andbutylene carbonate, and a low viscosity solvent which is selected fromthe group consisting of dimethyl carbonate, methyl ethyl carbonate,diethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran,1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane,1,2-dibutoxyethane, γ-butyrolactone, acetonitrile, methyl propionate,and dimethylformamide.
 9. A lithium secondary battery comprising apositive electrode, a negative electrode, and a non-aqueous electrolyticsolution which comprises a non-aqueous solvent and an electrolyte whichfurther contains 0.001 to 0.8 weight % of a biphenyl derivative havingthe following formula:

in which each of Y¹ and Y² independently represents a hydroxyl group, analkoxy group, a hydrocarbyl group, a hydrogen atom, an acyloxy group, analkoxycarbonyloxy group, an alkylsulfonyloxy group or a halogen atom,and each of p and q independently is an integer of 1 to
 3. 10. Thelithium secondary battery of claim 9, wherein the biphenyl derivative inthe non-aqueous electrolytic solution has the following formula:

in which Y represents a hydroxyl group, an alkoxy group, a hydrocarbylgroup, a hydrogen atom, an acyloxy group, an alkoxycarbonyloxy group, oran alkylsulfonyloxy group.